REPORT ON ATMOSPHERIC CIRCULATION. 



25 



Variation of the Force of the Wind. — During the cruise of the Challenger, 

 observations of the force of the wind were made on 1202 days, at least twelve 

 times daily, 650 of the days being on the open sea, and 552 near land. The observa- 

 tions were on Beaufort's scale 0-12, being the scale of wind force observed at sea. 

 The results showing the hourly variations in the force of the wind are given in 

 the following table, where the observations have been grouped according to the five 

 oceans in which they were made, viz. : the North Atlantic, the South Atlantic, the 

 North Pacific, the South Pacific, and the Southern Ocean : — 



Thus the velocity of the wind is greater over the open sea than on or near land, the 

 mean difference being from four to five miles per hour. Of the five oceans, the velocity 

 is greatest over the Southern Ocean, and least over the North Pacific, the difference 

 being eight miles per hour. In the part of the cruise embracing the Southern Ocean, 

 the Challenger crossed and re-crossed the " roaring forties," and hence probably the 

 higher observed velocity of the wind over this ocean. 



With respect to the open sea, it is evident from the mean curve for the five 

 oceans (Plate II. fig. 22) that the diurnal variation is very small, there being 

 apparently two indistinctly marked maxima about midday and midnight respectively. 

 But on examining the separate means of each of the five oceans, there appears to be 

 no uniform agreement observable among their curves, the slight variations being 

 different in each case. Looking at the curves in connection with the number of 

 observations from which each has been drawn, it seems probable that the line 

 representing the true diurnal variation in the velocity of the wind is practically a 

 uniform straight line, with the single exception of a small rise about midday, not quite 

 amounting to a mile per hour. 



(PHYS. CHEM. CHALL. EXF. — rART V. — 1889.) 4 



